Absolute measurement of vacuum ultraviolet photon flux in an inductively coupled plasma using a Au thin film

A new method for absolute measurement of the vacuum ultraviolet (VUV) photon flux at the edge of a plasma is described. The light produced by the plasma was allowed to strike a negatively biased, gold-coated copper substrate remote from the plasma. The resulting photoelectron emission current was measured, and the absolute photon flux was then found from the known photoelectron yield of Au. The method was used to quantify the amount of VUV light produced by an Ar/He inductively coupled plasma (ICP). Strong emissions at 104.82 and 106.67 nm, corresponding to the 1s(2) and 1s(4) resonant states of Ar, were observed. The maximum, integrated VUV photon flux measured at the remote location was 3.2 x 10(13) photons/cm(2) s. This was estimated to correspond to a flux of 5 x 10(15) photons/cm(2) s at the edge of the ICP, in the range of reported values under similar conditions.